1. Field of the Invention
The present invention relates to a flat plate laminate ozone generating apparatus including a plurality of laminated plate-shaped high voltage electrodes and low voltage electrodes between which an alternating voltage is applied to produce a discharge and generate ozone gas, and in particular, to an ozonizer which is an essential portion of the flat plate laminate ozone generating apparatus and which includes the high voltage electrodes and low voltage electrodes and to which oxygen is supplied to generate ozone gas.
2. Description of the Related Art
FIG. 27 is a cross sectional drawing of a conventional ozonizer described in, for example, Japanese Patent Publication No. 3113885 “Discharge Cell for Ozone Generator”. In a conventional ozonizer, as shown in FIG. 27, a plurality of low voltage electrodes 7 composed of approximately flat plate-shaped rigid bodies sandwich a pair of block(s) 25 on both sides and are superposed in a thickness direction of the plates to construct a number of electrode module laminated bodies. The electrode module laminated bodies are secured between an electrode presser plate 22 and a base 24 by means of a plurality of fastening bolts 21 passing through both side portions thereof in the laminating direction.
Each electrode module comprises a pair of upper and lower low voltage electrodes 7, a pair of bilateral blocks 25 sandwiched between the low voltage electrodes 7, 7, dielectric unit(s) 30 disposed between the low voltage electrodes 7, 7 and situated at an inner side of the blocks 25, 25 and a plurality of elastic spacers 26 for forming a plurality of discharge gaps provided for forming discharge gap(s) 6 at both sides of the dielectric unit(s) 30. The elastic spacers 26 constitute rod-shapes of a circular cross-section extending in a direction orthogonal to the page.
The pair of bilateral blocks 25 is a rigid body of a conductive plate material such as stainless steel plate(s), and, by intervening the blocks between both side portions of the low voltage electrodes 7, a space of an equal gap amount is formed in the thickness direction of the block(s).
Also, (all of) the drawings are expanded in the vertical direction and actual thickness is extremely thin, for example, three mm or less in the case of the low voltage electrode 7, and three mm or less in the case of the block 25.
Cooling water passages 9 are formed inside the pair of upper and lower low voltage electrodes 7 and combine as a heat sink. Moreover, a cooling water passage 9 is also formed in blocks 25 of one side. The cooling water passages 9 inside the low voltage electrodes 7 are communicated with a cooling water inlet/outlet 12 provided in the base 24 via the blocks 25 in order to circulate cooling water as a coolant.
On the other hand, an ozone gas passage 8 is formed in a main surface of the low voltage electrode 7 facing the discharge gap 6 by means of, for example, etching and the like. The ozone gas passage 8 is communicated with an ozone gas outlet 11 provided in the base 24 via an ozone gas passage 8 formed in the blocks 25. Also, an oxygen gas inlet 10 for supplying oxygen gas to the discharge gaps 6 along a direction orthogonal to the page surface is provided at both side portions of discharge gaps 6.
The dielectric unit(s) 30 disposed in the space surrounded by the upper and low voltage electrodes 7 and the bilateral blocks 25 is a thin sheet shaped rigid body comprising a sandwiched structure of a high voltage electrode 3 sandwiched between a pair of upper and lower glass plates 5. The high voltage electrode 3 is a conductive thin sheet such as a stainless steel sheet and the like and a portion thereof is led outside as a feed terminal (not shown).
The discharge gap forming elastic spacers 26 provided for forming the discharge gap 6 at both sides of the dielectric unit 30 are thin resin wire rods of a circular cross-section having ozone resistance properties and resiliency, and are disposed in the discharge gaps at a predetermined interval. A thickness of each elastic spacer 26 (outside diameter) is set to be 5–6% larger than each gap amount of the discharge gaps 6 in a non-compressed state.
With such a setting, the elastic spacer 26 is compressed from above and below by the low voltage electrode 7 and the dielectric unit 30, and the dielectric unit 30 is resiliently pressed from above and below by an equal pressure by this compression and maintained in a central portion, in the vertical direction, of the above mentioned space. Consequently, the discharge gaps 6 of an equal gap amount are formed at both sides of the dielectric unit 30.
Moreover, in a case where rigid spacers are used instead of the elastic spacers 26, when the blocks 25 are fastened, of course, the rigid spacers used are of a smaller diameter than the elected discharge gap length (the height of the discharge gap in the laminating direction). Thus, the spacers are not compressed in the laminating direction in the discharge gaps.
Next, operation will be explained.
When an alternating high voltage is applied between the low voltage electrode 7 and the high voltage electrode 3, a dielectric barrier discharge is generated in the discharge gap 6 via a dielectric 5. Oxygen gas is dissociated to single oxygen atoms by this discharge, and, at roughly the same time, a three body collision is induced between these oxygen atoms, other oxygen molecules and a wall and the like and ozone gas is generated. By using this mechanism and continuously supplying oxygen gas to the discharge gaps 6, the ozone gas generated by the discharge may be continuously derived as ozonized gas from the ozone gas outlet 11.
An ozone generating efficiency derived from this discharge is normally, at most, 20%. That is to say, 80% of the discharge power heats the electrodes and is lost. Also, the generating efficiency of the ozone gas is dependent on the temperature of the electrode (strictly speaking, the temperature of the discharge gas), and the lower the temperature of the electrode the higher the generating efficiency. Hence, the electrodes are directly cooled with cooling water and the like or a rise in gas temperature in the discharge gaps 6 may be suppressed by shortening the gap length of the discharge gap 6, and the ozone generating efficiency is increased by increasing the electron temperature, ozone decomposition is inhibited and, as a result, an efficient ozonizer capable of deriving highly concentrated ozone gas may be provided.
In a conventional ozonizer of such a construction, electrode cooling is one sided cooling of the low voltage electrode 7 side and the high voltage electrode 3 is not cooled. Thus, in a case where the same (amount of) power is supplied, the temperature of the gas in the discharge gaps 6 is about four (4) times that of a both side method for cooling the high and low voltage electrodes. Since the amount of generated ozone which is decomposed is increased by this rise in gas temperature, the discharge power density input to the electrode must be further increased and the ozone gas cannot be efficiently generated.
Moreover, when using the elastic spacers 26, because there are electrons having sufficiently high energy in the discharge gaps 6 due to the discharge, the elastic spacers 26 which are formed of an organic material collide with the high energy electrons (discharge energy) by contact with this discharge and the chemical bond incurs separation damage. When the ozonizer is used in continuous operation, the elastic spacers 26 deteriorate in a short period of time compared to metal spacers and an even flow of gas is made impossible by this deterioration, and there are drawbacks in that efficiency is rapidly reduced and the service life of the apparatus is shortened.
Also, even in a case where elastic spacers made of an ozone resistant Teflon (registered trademark) are used, the above mentioned high energy electrons (discharge energy) collide and the chemical bond suffers separation damage. Further, even if a material which is generally “flame retardant material” in air is used, as in the case of highly concentrated ozone or oxygen gas atmosphere “combustible material”, there is a problem in that a sublimation reaction of the elastic spacers is activated by the discharge energy at a portion disposed to directly contact the discharge gap and clean ozone cannot be obtained.
On the other hand, in the case where the rigid spacers are used instead of the elastic spacers 26, they are, naturally, designed to be of a smaller diameter than the elected discharge gap length when being fastened via the blocks 25. Hence, when the discharge gaps 6 are tiny gaps and a high concentration of ozone is to be generated, a pressure loss of the gap partitioned by the spacers 26 for forming the discharge gaps (pressure loss of the tiny gaps between the dielectric 5 and the spacers 26 for forming the discharge gaps) is much smaller than the pressure loss of the discharge gas passages (pressure loss of the gas passages orthogonal to the page surface of FIG. 27). Thus, the even flow of gas is made difficult by the spacers 26 for forming the discharge gaps. Consequently, there are problems in that the ozone generating efficiency is degraded and the ozonizer cannot be made compact.
Generally, a fluid cannot be evenly flowed unless the pressure loss of the gap formed by the spacer 26 can be made approximately ten (10) times or more the pressure loss of the discharge passage portion. For example, when the discharge gap 6 is 0.1 mm, a gap between the thickness of the spacer 26 and the discharge gap must be highly precise. It is extremely difficult to manufacture the spacers 26 with this sort of precision and dispose them without contacting the discharge gap. For this reason, a large cost increase is incurred in order to manufacture the spacers 26 with good precision and inexpensive manufacture of the apparatus is impossible.
Moreover, in the conventional ozonizer constructed such as above, the electrode module including the pair of upper and lower low voltage electrodes 7, the bilateral blocks 25 sandwiched between these low voltage electrodes 7, 7, the dielectric units 30 positioned at the inner side of the blocks 25, 25 and disposed between the low voltage electrodes 7, 7, and the plurality of elastic spacers 26 for forming the discharge gap(s) provided at both sides of the dielectric unit 30 for forming the discharge gaps 6 is laminated as a plurality via the low voltage electrodes 7 and is secured between the electrode presser plate 22 provided on top and the base 24 provided at the bottom by the plurality of fastening bolts 21 as a fixing means passing through the electrode module at both side portions thereof in the laminating direction. That is, since the structure is such that the dielectric module held between the low voltage electrodes 7 is fastened at both ends thereof, both sides of the electrode module become fulcrums and the low voltage electrodes 7 which are supposed to be straight are deformed to a circular arc shape, and there is a problem in that, particularly in a discharge gap of 0.1 mm in thickness, the gap length cannot be even and highly concentrated ozone cannot be obtained.
Further, a conventional ozone passage 8 is manufactured without being gas sealed. Thus, 100% of the oxygen gas raw material cannot be supplied to each electrode module sandwiched by the laminated low voltage electrodes 7. That is, a “short pass phenomena” occurs in which oxygen gas escapes directly to the ozone gas outlet without passing through the discharge passage of the electrode module. When this “short pass phenomena” takes place, the ozone generating efficiency of the electrode module is reduced and highly concentrated ozone cannot be generated; further, since the concentration of the ozone generated by the discharge gap 6 is diluted by a short pass fluid flow of the raw material oxygen gas, there is a problem in that highly concentrated ozone gas cannot be further derived.